1. Field of the Invention
This invention relates to a means for drafting a fiber bundle such as a sliver or a roving. More specifically it relates to a means for drafting a fiber bundle, which is suitable for a high speed spinning machine such as a fasciated yarn spinning frame.
2. Description of the Prior Art
In the spinning process, a so-called roller drafting arrangement by which a fiber bundle is attenuated with a plurality of pairs of draft rollers rotating at sequentially higher peripheral speeds one after the other, has widely been utilized.
In the above-mentioned conventional drafting means, a concomitant air stream often occurs in the vicinity of the surface of the rotating roller. The speed of the air stream accelerates as the rotational speed of the roller increases, but if the speed of the roller exceeds 60 meters/min, the air stream disturbs the ribbon of the fiber bundle traveling through the draft zone between the two pairs of rollers. This causes a deterioration in the quality of the resulting yarn, especially in the case of a thin fiber bundle, as well as an increase in flies. These drawbacks are pronounced in the vicinity of front rollers rotating at the highest speed among the draft rollers.
Also, in the conventional drafting arrangement, various types of collectors are utilized between draft rollers for controlling the width of the ribbon of the fiber bundle, which tends to spread excessively due to a nipping pressure of the draft rollers; and a wider width of the fiber ribbon causes a separation in the edge portion fibers which may often wrap around the roller or form flies. Especially, in the fasciated yarn spinning process, the collector means is very important since the edge portion fibers have to twine around a core portion of the fiber bundle to form a tightly fasciated yarn.
However, since the conventional collector means is, in general, designed to function effectively at a speed less than 60 meters/min., it is not protected from the concomitant air stream around the circumference of the roller. For example, the conventional collector means is of a U-shape with an open top side and is short in length along the traveling direction of the fiber bundle. This form is not suitable for protecting the fiber bundle from the concomitant air stream. Especially in case of fasciated yarn spinning, when the operational speed exceeds 150 meters/min. poor results are obtained if the conventional collector means is utilized.